1. Field of the Invention
This invention relates to the use of high and low density brines in well bores, and it more particularly relates to the removal of solids, e.g., drilling residue and mud and solids and oil from such brines.
2. Description of the Prior Art
Aqueous brine solutions of high density are used in well bores employed in the production of petroleum. These solutions have been used as both drilling, completion and packer fluids especially in deep wells subject to high formation oil and gas pressures at elevated temperatures. These brines can be formed of the sodium, potassium, calcium and zinc salts with chloride and bromide ions. These aqueous fluids may include corrosion inhibitors and other salts such as soda ash. The density of these salt type well fluids depends on the particular salt, or mixture of salts, and their concentration in the aqueous well fluid. Usually, these salt type well fluids have a density in the range of between about 8 and 19 pounds per gallon.
The salt type well fluid should be solids-free in its use as a well fluid. If there are solids in a packer or completion fluid, they can cause serious injury to a producing formation by plugging of the pore spaces therein or even of the perforations and channels provided to induce fluid flows between the formation and well bore. If there are solids in a packer fluid, the solids will precipitate with time upon the packer. As a result, these solids deposit make it difficult to disconnect the tubing from the packer with a resultant costly well workover.
A process has been developed for removing the contaminating solids from high density, salt-type (brine) aqueous drilling, completion and packer fluids before their placement into a well bore. This process is described in our U.S. Pat. No. 4,456,537 and copending application Ser. No. 450,519 filed Dec. 17, 1982, which patent and application for descriptive purposes is incorporated herein. Thus, the solids contaminated brine can be cleaned by our unique process, specifically before it enters the surface equipment of the well system.
Although the brine can be made solids-free at the rig, it is preferred to clean the well system of drilling fluid or mud solids oil, etc. before introduction of the brine into it. One of the main problem areas in removing drilling fluid is from residues in the well bore equipment which includes the tubing or well pipe and the annulus between it and the casing or surrounding well bore.
In accordance with our process described in U.S. Pat. No. 4,474,240, there is provided an improved displacement process for eliminating drilling fluid components of mud, solids and oil from well bore equipment prior to introduction of solids-free completion and packer brine. The drilling fluid is displaced from the well bore equipment by a treated water plug circulated at turbulent flow through the well bore equipment for displacing drilling fluid and other solids before it. The treated water removes residual drilling fluid and it has a novel composition of surfactant and alcohol in clean water subjected to agitation and shear mixing. After the treated water, the solids-free brine is introduced into the well bore equipment.
In other embodiments, a plug of gelled aqueous spacer can be introduced before or after the treated water. Where the drilling fluid is inverted, the spacer preferably precedes the treated water and comprises an inverted gel formed of bentone, water and diesel oil. In other cases, the aqueous spacers can contain a viscosifier polymer such as hydroxyethylcellulose (HEC). Preferably, an aqueous spacer precedes and follows the plug of treated water.
As a result, the drilling fluid, spacers and treated water leave the well bore equipment clean for the brine introduced therein in a solids-free condition. The plugs and treated water can be specially composed so that the former travel at laminar flow and the latter at turbulent flow in the well bore equipment at the same ranges of linear velocity.
In the present improved process, the brine is any solution of the mentioned salts and water, and the solids content of the brine to be treated is not greater than 1-2 percent by weight depending on the brine's density and the specific gravity of the solids. Greater amounts of solids should be removed by retreating the brine by the Dirt Magnet.RTM. Process of the U.S. Pat. No. 4,456,537 and copending application Ser. No. 450,519, filed Dec. 17, 1982.
The contaminating solids are usually introduced into the well bore by inadvertent passage of the solids-free brine through uncleaned "dirty valve or pumping conduit" which had relatively large residual amounts of drilling mud or like solids. Once these solids enter the well bore, they would settle to the bottom of the well bore. These settled solids if adjacent a production zone of interest create undesired problems relative to completion procedures such as acoustic logging and perforation techniques. For example, the solids shield or obscure the camera-like picture of acoustic logging. Most importantly, these settled solids will enter perforations, especially as they are made, to seal or plug channels in the production formations. Other problems from the settled solids will be apparent to those working in these art areas.
The present improved process removes the settled solids from the brine at the production zone of interest without reprocessing the entire brine within the well bore.